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#1 |
Senior Member
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Location: Lexington, Ky
Posts: 2,133
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Over heating question
Drove 20 miles to the local cruise last night with the a/c running. Temp gauge normal, running a fairly new 160 thermostat (72 350 automatic). I opened the hood upon arrival and everything under the hood was hot. The hood release latch was even hot, as were the inner fenders, radiator support, etc.
Read one thread that said you could bleed air out of the cooling system, can someone tell me how to do that ?? Noticed that my fan blade will turn easily with the engine not running. Is that normal. Bad fan clutch? Didn't check the lower radiator hose while it was hot, will maybe do that today. Lower hose collapsing? Puzzled that my temp gauge is normal but seems hotter than a firecracker under the hood. Seems to run fine but now afraid to drive it much. Any help appreciated.
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Larry 84 Chevy SWB, "Roy", dark blue orig paint, 6 cyl auto, PS, 88,000 miles. 72 Highlander LWB "Olive" med olive over lt yellow, air, 77,000 miles (sold) "It's a sorry man who can't find his wife a good job" |
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#2 |
Registered User
Join Date: Nov 2014
Location: Bigfork, Montana
Posts: 1,137
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Re: Over heating question
your 350 will "self bleed" if you've driven any distance at all the cooling system is bled
if the fan clutch is turning without any resistance when the engine is cold, replace it. it should have moderate resistance when turned by hand (engine off - do I really need to say this!?) if the lower hose was collapsing you would have seen higher temperatures at the gauge so it's probably not the problem what was the ambient temp when you drove it? the radiator is getting rid of a lot of heat, everything under the hood will heat up in high ambient temps (I know you know this, just saying it anyway) I would confirm the temp gauge is reading correctly using a laser temp gun. you can "shoot" the thermostat housing for an accurate temp. it's actually kinda cool (pun intended) you can "see" the thermostat open & close if you hold the gun steady (it's that accurate!) if the radiator isn't boiling over & the temp gauge is accurate, i would just change the clutch Bobby |
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#3 |
Registered User
Join Date: Aug 2006
Location: Redmond, WA
Posts: 6,332
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Re: Over heating question
I would invest in a cheap IR thermal gun to sanity check what you're seeing at the gauge. If the thermostat housing is 190 when the gauge is normal, that's fine. But if the temp is 230 and the gauge is reading normal, you need to know that. Right now you can only assume the gauge is right. Might as well know for sure, and there's a million other uses for the temp guns, a good investment.
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1970 GMC Sierra Grande Custom Camper - Built, not Bought 1969 Pontiac 2+2 427/390 4-speed Coupe 1969 Pontiac 2+2 427/390 4-speed Convertible |
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#4 |
20' Daredevil (Ret)
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Location: Jefferson State
Posts: 13,635
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Re: Over heating question
It's hard to describe in print how easily or how hard it is to turn the fan. You should be able to rotate it easily, but there should be resistance -- like it's mired in molasses, if that helps. If you can spin it quickly, or if it spins even a little after you take your hand off of it, the clutch is bad.
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- Mike - 1972 K20 LWB 350/350/205 RIP El Jay |
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#5 |
Registered User
Join Date: Aug 2006
Location: Redmond, WA
Posts: 6,332
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Re: Over heating question
I'd say you shouldn't be able to get more than about half a rotation after you let go of the fan. If you can spin it hard by hand and it goes all the way around, that'd be too much.
That's a real ballpark answer, and it's a big ballpark, but a full spin would be over the wall, as it were...
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1970 GMC Sierra Grande Custom Camper - Built, not Bought 1969 Pontiac 2+2 427/390 4-speed Coupe 1969 Pontiac 2+2 427/390 4-speed Convertible |
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#6 |
20' Daredevil (Ret)
![]() Join Date: May 2003
Location: Jefferson State
Posts: 13,635
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Re: Over heating question
Your experiences may have been a bit different than mine..... I have never had a fan spin freely, even a little, after I let go of it. Just my 2 cents
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- Mike - 1972 K20 LWB 350/350/205 RIP El Jay |
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#7 |
Registered User
Join Date: Sep 2009
Location: Lafayette, Indiana
Posts: 339
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Re: Over heating question
I've been struggling with some over heating problems lately myself. My truck has a Pontiac 400 instead of a SBC 350 though. I was running 220 when driving around town.
I bought an IR thermometer to see what temp I was running because I didn't trust the aftermarket gauge I was using. I replaced my 180 degree thermostat with a new 180 degree thermostat. I installed a fan shroud and clutch fan (mine didn't have one and I had to hack it to pieces to get it to fit the Pontiac accessories. I checked and reset my timing. I tuned my carb to not run a lean Air/Fuel mixture. Now my truck doesn't climb over 200 on the gauge and IR thermometer even when idling in the driveway for 30-40 mins.
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1969 CST/10 "GreenAndWhite" 1974 Nova (SOLD... End of an Era) 2000 Impala (RIP) 2008 Malibu Brand Loyal... I've never owned a Vehicle not made by Chevrolet. |
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#8 |
Senior Member
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Location: Lexington, Ky
Posts: 2,133
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Re: Over heating question
'Thank you' to each of you who have replied, good input from all.
I replaced the fan clutch today, $30 and an hour labor, but it didn't help. I'm buying a cheap IR thermal gun off ebay as was suggested. Will post results in a few days . Thanks again.
__________________
Larry 84 Chevy SWB, "Roy", dark blue orig paint, 6 cyl auto, PS, 88,000 miles. 72 Highlander LWB "Olive" med olive over lt yellow, air, 77,000 miles (sold) "It's a sorry man who can't find his wife a good job" |
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#9 |
Registered User
Join Date: Sep 2010
Location: Los Angeles California
Posts: 352
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Re: Over heating question
Try a higher temperature thermostat.
Strange as it seems.. The higher the thermostat, the cooler your engine will run. J.
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1972 Custom Deluxe Highlander C20 1971 Javelin SST New Project 1971 Demon 340 1969 SS El Camino 1968 SS RS 396 Camaro 1967 Barracuda Formula S 1965 140/4sp Corvair Monza Convertible Sorry, but I don't do Fords. |
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#10 | |
Registered User
Join Date: May 2016
Location: Henderson NC
Posts: 975
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Re: Over heating question
Quote:
I found that you need water circulating through the heater core for these motors to cool properly. I have a leak in my heater core so I plugged the ports off when I installed my new crate motor. The temp would be fine for 10 or 15 miles then it would jump to the hot side and back to normal. I installed a by-pass hose where the heater hoses should be and it runs constant on the low side of normal now. I have a new heater core and will be installing it asap. |
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#11 |
Special Order
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Location: Mt Airy, MD
Posts: 85,859
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Re: Over heating question
Mine seems a bit hotter than it should be, too. The air filter housing gets too hot to handle. My circuit board is fried and I need to get to that, but I am sure it is hotter than usual. I have a 180 deg t-stat. It's new and I tested the old one which is still fine. I had an issue a few years ago that resulted in new fan clutch, water pump, and it ended up being poor flow through the radiator. I took another one (4 core) to the radiator shop for the royal treatment. It ran nice and cool after that. Now, with fresh heads, a freshly rebuilt carb, tune up, fresh hoses, and plug wires after it gets up to temp and I shut it off, after a few minutes it just cranks it's butt off without a kick at all. Let it cool down and runs like a top. I suspect ethanol poisoning since it sat since May '15 till a couple weeks ago, combined with extra heat. But why so warm? I need to go through it all and try other timing/carb adjustment. Maybe a weak diaphram in the fuel pump not pumping well once warm. i already replaced the ign module, and it starts on starter fluid, so not the coil. I need to put some time into it son. I hoped to get a clue to it's running hot issue here. It isn't over heating, either. I loaded it up with a loaded trailer and went 75 miles with two mountains to cross and it did fine. Just don't shut it down unless you have 20-30 minutes to spare.
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"BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~ |
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#12 | |
Registered User
Join Date: Sep 2010
Location: Los Angeles California
Posts: 352
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Re: Over heating question
Quote:
It kind of runs contrary to having A/C on though.. As to the thermostat.. A thermostat only has one function, to open at a set heat level. If your engine overheats, that is heats up beyond the level of the thermostat, the thermostat just remains open, and the water flows constantly, not having any chance to cool off. The thermostat actually helps the radiator. It keeps the water in the radiator longer, if the temperature on the Thermostat is higher. Longer time in the radiator, the longer it has to cool down BELOW the level of the thermostat. As long as the hot water temp is lower flowing back into the engine, the hotter water in the radiator has longer to cool down. The fan and shroud help lower the temp in the radiator faster.. and hopefully before the water in the engine gets hot enough to open the thermostat. If this happens, the radiator gets flooded with hot water, and ruins the water you're supposed to cool.. this means hot water above the thermostat temp is flowing back into the engine, and the thermostat won't be triggered to close. Hot water is now flowing freely through the system without getting a chance to cool down, and continues to rise until steam pressure breaks a hose seal, or pops the pressure limit on the radiator cap. So adding a higher temperature thermostat actually keeps the water in the radiator longer. Giving it more time to cool down. Sometimes all you need is that extra 10 or 20 degrees. J.
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1972 Custom Deluxe Highlander C20 1971 Javelin SST New Project 1971 Demon 340 1969 SS El Camino 1968 SS RS 396 Camaro 1967 Barracuda Formula S 1965 140/4sp Corvair Monza Convertible Sorry, but I don't do Fords. |
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#13 | |
Registered User
Join Date: Sep 2010
Location: Los Angeles California
Posts: 352
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Re: Over heating question
Quote:
Circulation is important, but the motor/radiator is actually a simple heat exchanger. It's more important to cool the water in the radiator below the temp of your thermostat. Otherwise you may as well remove it, as it's not doing the job. One more thing is radiator capacity. It's important to have at least an equal amount of water in the radiator, that can exchange for the hot water in the block. People also notice that the temperature gauge will go high, then fall, and repeat. This is normal, because when the radiator closes, the water in the block stops moving, and starts to take on heat. When it gets hot enough, the thermostat opens, and THEN the water flows past, and fills the radiator, displacing the cooler water. J.
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1972 Custom Deluxe Highlander C20 1971 Javelin SST New Project 1971 Demon 340 1969 SS El Camino 1968 SS RS 396 Camaro 1967 Barracuda Formula S 1965 140/4sp Corvair Monza Convertible Sorry, but I don't do Fords. Last edited by JCD; 08-13-2016 at 10:41 PM. |
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#14 |
Special Order
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Location: Mt Airy, MD
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Re: Over heating question
The clutch and even fan only come into play, for cooling, when air flow from traveling is low. Such as sitting, stop and go, or moving steadily at a very low speed. The purpose of the clutch is to "disengage" the fan when not needed vs constant fan. It's about less drag on the engine for power and economy.
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"BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~ |
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#15 |
20' Daredevil (Ret)
![]() Join Date: May 2003
Location: Jefferson State
Posts: 13,635
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Re: Over heating question
^^ Under 'normal' circumstances, yes..... but a fan clutch will engage whenever high temps call for it, even with reasonably good airflow. Example: going uphill, esp. with a heavy load. You might be doing 45-50 mph but the engine temps rise and the fan engages. I've had it happen many times with my pickup as well as several trucks at work. Hot weather and a long 6% plus grade will do that. Come to think of it, I've also had it happen on flat ground at highway speed in very hot weather. No fun at all in a truck with no A/C.
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- Mike - 1972 K20 LWB 350/350/205 RIP El Jay |
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#16 | ||
"I ain't nobody, dork."
Join Date: Sep 2007
Location: Whidbey Island, Washington
Posts: 8,940
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Re: Over heating question
When I read "overheating" I immediately think of a vehicle sitting on the side of the road puking coolant out of it. If that's not the case, then a rig is just running a little hotter than normal. But...
If you're running around 200 degrees, I would say that's close to normal operating temp as the thermostat does it's job. I agree that running a 160 degree thermostat won't help. Heck even newer rigs run at operating temps of 200 to 215 degrees. Also depending on what the heat index is where you live, is probably not helping matters. Gary
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'cuz chicks dig scars... My 1972 GMC 1500 Super Custom (Creeping Death) "long term" build thread. The Rebuild of Creeping Death after the wreck Quote:
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#17 |
Rottenwood Garage Member
Join Date: May 2005
Location: Marietta, Georgia
Posts: 4,321
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Re: Over heating question
When we have them run warm or hot, the first thing we do is check the temp with a laser gauge, check and set the timing, put thermostat in a pot of water on the stove, throw a replacement radiator in it off the shelf and check the water flow to make sure the water pump is working.
On the junk we bring home most of the times its timing or a "clogged up" radiator.
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2004 Chevrolet Suburban C1500 2001 Chevrolet 2500HD Crew 6.0 1999 Harley Davidson Electra Glide 1972 Chevrolet C-20 Custom Camper "Dump Truck" 1972 Chevrolet C-20 Suburban "Big Green" 1969 Chevrolet C-50 Wedge Hauler "Leonidis" 1966 C-10 2x4 short fleet 327 4 speed "Race Truck" 1952 Plymouth Cranbrook "Rican" (my grandfathers) 1931 Ford Model A Coupe "Black Beauty" 1930 Ford Model A truck "Club Cab" 4x4 Rottenwood Garage and Speed Shop.....where everything must be racy! It's not just a hobby..It's a LIFESTYLE!!! Thanks for nothing Barrett-Jackson You cant fix stupid or teach accountability! Time wasters, looky Lous and tire kickers are everywhere! |
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#18 | |
Registered User
Join Date: May 2016
Location: Henderson NC
Posts: 975
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Re: Over heating question
Quote:
The reason for needing the heater core circulating is to get more flow through the heads. Water needs to circulate from the intake below the thermostat to the water pump either through the heater core or a by-pass hose. This keeps the heads cool until the thermostat opens and increases the flow through the heads even after the thermostat opens. |
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#19 |
Registered User
Join Date: Aug 2006
Location: Redmond, WA
Posts: 6,332
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Re: Over heating question
One day I'm going to write a really big and long manifesto out in my Unabomber-style shack on two things:
"The Myth of Slowing Coolant Down - Why Faster is Better" and "The Sin of Connecting Your Vacuum Advance to Manifold Vacuum" Both of these evil lies must be stopped. But today is not the day. For now, just know that "slowing coolant down so it has time to cool in the radiator" is not a real thing. One day, many decades ago, a drag racer fixed water pump cavitation by installing a restrictor plate in an engine that lacked a thermostat and somehow the legend took hold. But that was pump cavitation, something completely separate. You want to pump it as fast as you can without cavitation. Thermostats are there to set the low point - then they open. Higher thermostats will not cool better, cooler thermostats will not keep an engine cooler if the fan/rad package can't hold the temp constant at or below the thermostat open point.
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1970 GMC Sierra Grande Custom Camper - Built, not Bought 1969 Pontiac 2+2 427/390 4-speed Coupe 1969 Pontiac 2+2 427/390 4-speed Convertible Last edited by davepl; 08-14-2016 at 05:32 PM. |
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#20 | |
Registered User
Join Date: Sep 2014
Location: USA
Posts: 2,249
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Re: Over heating question
Quote:
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#21 | |
Special Order
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Location: Mt Airy, MD
Posts: 85,859
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Re: Over heating question
Quote:
I know my cooling system is fine and when the heads and manifold were off the engine was clean as a whistle. New heads are 64cc 1.94" where old heads were stock '72 truck. Mine's probably the higher compression (maybe slight heat increase), timing, carb adjustment, and maybe even plug heat range(?) combined with possibly a weak fuel pump or ethanol issues. It just cranks when warm till cools down and also starves when warm when I hit it. I didn't have time to get into it this weekend. Meanwhile I'm putting a wood base gasket under the carb and checking filter. I want to pull the seat and check the sock in the tank, too, maybe pull tank and flush. I feel it's a little heat and a little fuel delivery. It's not starting as eagerly as at first when cold either, so likely my friend ethanol mud paying me (and my fresh carb) a visit EDIT: I also drilled an 1/8" hole in the thermostat
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"BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~ Last edited by special-K; 08-15-2016 at 07:14 AM. |
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#22 | |
Registered User
Join Date: Sep 2010
Location: Los Angeles California
Posts: 352
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Re: Over heating question
Quote:
More flow..ie, when a thermostat fails, or remains open.. is when overheating occurs even on a highway, with the most cool air running through a radiator. The engine doesn't rely on water being cooled in the heater core, as the air doesn't flow through until you turn on the heater fan. You can read the basics here. http://www.stant.com/index.php/engli...rmostats/faqs/ J.
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1972 Custom Deluxe Highlander C20 1971 Javelin SST New Project 1971 Demon 340 1969 SS El Camino 1968 SS RS 396 Camaro 1967 Barracuda Formula S 1965 140/4sp Corvair Monza Convertible Sorry, but I don't do Fords. |
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#23 |
Special Order
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Location: Mt Airy, MD
Posts: 85,859
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Re: Over heating question
I understand how the system works. The system is all about circulation through the radiator for cooling. It's that simple. No circulation/no cooling. People only replace a thermostat that sticks open to get heat, they replace one stuck shut to get cooling
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"BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~ |
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#24 | |
Registered User
Join Date: May 2016
Location: Henderson NC
Posts: 975
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Re: Over heating question
Quote:
If you have a vortec engine or one with vortec heads you have to have a bypass for the heads because the water pump bypass is blocked. This is true for a lot of after market heads also. I have studied this quite a bit. |
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#25 |
Senior Member
![]() Join Date: Oct 2012
Location: Lexington, Ky
Posts: 2,133
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Re: Over heating question
Update on original problem:
I bought a cheap Heat Thermal Gun as suggested by Davepl. My temp at the Themostat housing measured 175 which matches my 170 themostat. Long story short, I think your engine and surroundings get hotter after the engine is turned off. With 90 degree heat and high humidity, I think I panicked and imagined a problem that didn't exist. So I think everything is actually fine. If anyone can use a Raytek MT4 Mini Temp gun thermometer for $35 shipped, let me know cause I doubt if I will need it again. (that is what I paid for it). I appreciate all replies and opinions trying to help. Thank You !!
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Larry 84 Chevy SWB, "Roy", dark blue orig paint, 6 cyl auto, PS, 88,000 miles. 72 Highlander LWB "Olive" med olive over lt yellow, air, 77,000 miles (sold) "It's a sorry man who can't find his wife a good job" |
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